Testing and Commissioning of MV/HV
Cables
Example of asbestos paper insulation wrap on high-voltage cable inside an underground cable vault. Several layers of
the soft and friable insulation are wrapped around the cable in long, wide strips. Originally, pure white, the discoloration is
from sediment mud after formerly being submerged in the once flooded vault; some water leakage is still present.
1. Visual and Mechanical Inspection
1. Compare cable data with drawings and specifications.
2. Inspect exposed sections of cables for physical damage.
3. Inspect bolted electrical connections for high resistance using one or more of the
following methods:
1. Use of a low-resistance ohmmeter in accordance with Section 1.2 above.
2. Verify tightness of accessible bolted electrical connections by calibrated torquewrench method in accordance with manufacturer’s published data or Table 100.12.
3. Perform a thermographic survey.
(NOTE: Remove all necessary covers prior to thermographic inspection. Use
appropriate caution, safety devices, and personal protective equipment.)
4. Inspect compression-applied connectors for correct cable match and indentation.
5. Inspect shield grounding, cablesupports, and terminations.
6. Verify that visible cable bends meet or exceed ICEA and manufacturer’s minimum
published bending radius.
7. Inspect fireproofing in common cable areas. (**)
8. If cables are terminated through window-type current transformers, inspect to verify that
neutral and ground conductors are correctly placed and that shields are correctly
terminated for operation of protective devices.
9. Inspect for correct identification and arrangements.
10. Inspect cable jacket and insulation condition.
** Optional test
2. Electrical Tests
1. Perform resistance measurements through bolted connections with a low-resistance
ohmmeter, if applicable, in accordance with Section 1.1.
2. Perform an insulation-resistance test individually on each conductor with all other
conductors and shields grounded. Apply voltage in accordance with manufacturer’s
published data. In the absence of manufacturer’s published data, use Table 100.1.
3. Perform a shield-continuity test on each power cable.
4. In accordance with ICEA, IEC, IEEE and other power cable consensus standards, testing
can be performed by means of direct current, power frequency alternating current, or very
low frequency alternating current. These sources may be used to performinsulationwithstand tests, and baseline diagnostic tests suchas partial discharge analysis, and
power factor or dissipation factor. The selection shall be made after an evaluation of the
available test methods and a review of the installed cable system.
.
Some ofthe available test methods are listed below:
.
1. Dielectric Withstand:
1. Direct current (DC) dielectric withstand voltage
2. Very low frequency (VLF) dielectric withstand voltage
3. Power frequency (50/60 Hz) dielectric withstand voltage
2. Baseline Diagnostic Tests:
1. Power factor/ dissipation factor (tan delta):
1. Power frequency (50/60 Hz)
2. Very low frequency (VLF)
2. DC insulation resistance:
3. Off-line partial discharge:
1. Power frequency (50/60 Hz)
2. Very low frequency (VLF)
3. Test Values
3.1 Test Values – Visual and Mechanical
1. Compare bolted connection resistance values to values of similar connections.
Investigate values which deviate from those of similar bolted connections by more than 50
percent of the lowest value.
2. Bolt-torque levels should be in accordance with manufacturer’s published data. In the
absence of manufacturer’s published data, use Table 100.12.
3. Results of the thermographic survey.
(NOTE: Remove all necessary covers prior to thermographic inspection. Use appropriate
caution, safety devices, and personal protective equipment.)
4. The minimum bend radius to which insulated cables may be bent for permanent training
shall be in accordance with Table 100.22.
3.2 Test Values – Electrical
1. Compare bolted connection resistance values to values of similar connections.
Investigate values which deviate from those of similar bolted connections by more than 50
percent of the lowest value.
2. Insulation-resistance values shall be in accordance with manufacturer’s published data. In
the absence of manufacturer’s published data, use Table 100.1.Values of insulation
resistance less than this table or manufacturer’s recommendations should be investigated.
3. Shielding shall exhibit continuity. Investigate resistance values in excess of ten ohms per
1000 feet of cable.
4. If no evidence of distress or insulation failure is observed by the end of the total time of
voltage application during the dielectric withstand test, the test specimen is considered to
have passed the test.
5. Based on the test methodology chosen, refer to applicable standards or manufacturer’s
literature for acceptable values.
Tables
Table 100.12.1
Bolt-Torque Values for Electrical Connections
- US Standard Fasteners (a)
- Heat-Treated Steel – Cadmium or Zinc Plated (b)
Table 100.12.1 - Bolt-Torque Values for Electrical Connections
a) Consult manufacturer for equipment supplied with metric fasteners.
b) Table is based on national coarse thread pitch.
Table 100.12.2
- US Standard Fasteners (a)
- Silicon Bronze Fasteners (b, c)
Torque (Pound-Feet)
Torque (Pound-Feet)
a) Consult manufacturer for equipment supplied with metric fasteners.
b) Table is based on national coarse thread pitch.
c) This table is based on bronze alloy bolts having a minimum tensile strength of 70,000 pounds
per square inch.
Table 100.12.3
- US Standard Fasteners (a)
- Aluminum Alloy Fasteners (b, c)
Torque (Pound-Feet)
Torque (Pound-Feet) - Aluminum Alloy Fasteners
a) Consult manufacturer for equipment supplied with metric fasteners.
b) Table is based on national coarse thread pitch.
c) This table is based on aluminum alloy bolts having a minimum tensile strength of 55,000 pounds
per
square inch.
Table 100.12.4
- US Standard Fasteners (a)
- Stainless Steel Fasteners (b, c)
Torque (Pound-Feet)
Torque (Pound-Feet) - Stainless Steel Fasteners
a) Consult manufacturer for equipment supplied with metric fasteners.
b) Table is based on national coarse thread pitch.
c) This table is to be used for the following hardware types:
 Bolts, cap screws, nuts, flat washers, locknuts (18-8 alloy)
 Belleville washers (302 alloy).
Tables in 100.12 are compiled from Penn-Union Catalogue and Square D Company, Anderson
Products Division, General Catalog: Class 3910 Distribution Technical Data, Class 3930
Reference Data Substation Connector Products.
Table 100.1
Insulation Resistance Test Values Electrical Apparatus and Systems
Table 100.1 - Insulation Resistance Test Values Electrical Apparatus and Systems
In the absence of consensus standards dealing with insulation-resistance tests, the Standards
Review Council suggests the above representative values. Test results are dependent on the
temperature of the insulating material and the humidity of the surrounding environment at the time
of the test.
Insulation-resistance test data may be used to establish a trending pattern. Deviations from the
baseline information permit evaluation of the insulation.
Table 100.22
Minimum Radii for Power Cable
Single and Multiple Conductor Cables with Interlocked Armor, Smooth or Corrugated Aluminum
Sheath or Lead Sheath
Table 100.22 - Minimum Radii for Power Cable
ANSI/ICEA S-93-639/NEMA WC 74-2000, 5-46 kV Shielded Power Cable for Use in the
Transmission and Distribution of Electric Energy, Appendix I – Recommended Bending Radii for
Cables and Table I1 – Minimum Radii for Power Cable.
a. 12 x individual shielded conductor diameter, or 7 x overall cable diameter, whichever is greater.
Resource: STANDARD FOR ACCEPTANCE TESTING SPECIFICATIONS for Electrical Power
Equipment and Systems (NETA 2009)
Source:
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